package com.lagou.sqlSession;

import com.lagou.pojo.Configuration;
import com.lagou.pojo.MappedStatement;

import java.lang.reflect.*;
import java.util.List;

public class DefaultSqlSession implements SqlSession {
    private Configuration configuration;

    public DefaultSqlSession(Configuration configuration) {
        this.configuration = configuration;
    }

    @Override
    public <E> List<E> selectList(String statementId, Object... params) throws Exception {
        //将要去完成对simpleExecutor里的query方法的调用
        SimpleExecutor simpleExecutor = new SimpleExecutor();
        MappedStatement mappedStatement = configuration.getMappedStatementMap().get(statementId);
        List<Object> list = simpleExecutor.query(configuration, mappedStatement, params);
        return (List<E>) list;
    }

    @Override
    public <T> T selectOne(String statementId, Object... params) throws Exception {
        List<Object> objects = selectList(statementId, params);
        if (objects.size() == 1)
            return (T) objects.get(0);
        else {
            throw new RuntimeException("查询结果为空或者返回结果过多");
        }
    }

    @Override
    public int update(String statementId, Object... params) throws Exception {
        SimpleExecutor simpleExecutor = new SimpleExecutor();
        MappedStatement mappedStatement = configuration.getMappedStatementMap().get(statementId);
        return simpleExecutor.update(configuration, mappedStatement, params);
    }

    @Override
    public <T> T getMapper(Class<?> mapperClass) {
        //使用jdk动态代理来为dao接口生成代理对象并返回
        Object proxyInstance = Proxy.newProxyInstance(DefaultSqlSession.class.getClassLoader(), new Class[]{mapperClass}, new InvocationHandler() {
            @Override
            public Object invoke(Object o, Method method, Object[] args) throws Throwable {
                //底层依旧是执行jdbc代码  根据不同情况，来调用selectList或者selectOne
                //准备参数 1：statementId：sql语句的唯一标识：namespace.id= 接口全限定名.方法名
                String methodName = method.getName();//方法名
                String className = method.getDeclaringClass().getName();//接口全限定名
                String statementId = className + "." + methodName;

                //准备参数2：params：args
                //获取当前被调用方法的返回值类型
                Type genericReturnType = method.getGenericReturnType();
                //判断是否进行了 泛型类型参数化
                if (genericReturnType instanceof ParameterizedType) {
                    List<Object> objects = selectList(statementId, args);
                    return objects;
                }
                //判断返回值是否是int类型
                else if (genericReturnType.getTypeName().equals("int")) {
                    return update(statementId, args);
                }
                return selectOne(statementId, args);
            }
        });
        return (T) proxyInstance;
    }
}
